JP2014533471A - Initial acquisition and proximity search algorithms for wireless networks - Google Patents

Abstract

In a wireless network, a base station (BS) may transmit a primary synchronization signal (PSS) and a secondary synchronization signal (SSS). These synchronization signals may be used by the UE for cell detection and acquisition. In a typical search operation, first, a PSS sequence transmitted by a neighboring BS may be found, and then SSS detection may be performed. This specification further describes an algorithm for detecting PSS and SSS from the BS. A method for detecting BS samples a received signal from a receiver antenna to obtain a sampled sequence, analyzes the sampled sequence to detect a PSS in the current half frame (HF), and is detected Calculate signal-to-noise ratio (SNR) metrics based on the PSS, combine the calculated SNR with the SNR metrics obtained from the previous half frame, analyze the combined SNR metrics to obtain timing information, and The method generally includes analyzing the sampled sequence using the information to detect SSS.

Description

CROSS REFERENCE TO RELATED APPLICATIONS This application is a US Provisional Patent Application No. 61 filed Nov. 10, 2011 having the name “Initial Acquisitoin And Neighbor Search Algorithms For Wireless Networks”, which is incorporated herein by reference. / 558,377 claims the benefit.

  Certain aspects of the present disclosure relate generally to wireless communications, and more particularly to algorithms for initial acquisition and proximity search of a wireless network.

  Wireless communication networks are widely deployed to provide various communication services such as voice, video, packet data, messaging, broadcast, and so on. These wireless networks can be multiple access networks that can support multiple users by sharing available network resources. Examples of such multiple access networks include code division multiple access (CDMA) networks, time division multiple access (TDMA) networks, frequency division multiple access (FDMA) networks, orthogonal FDMA (OFDMA) networks, and single carrier FDMA ( SC-FDMA) network.

  A wireless communication network may include a number of base stations (BSs) that can support communication for a number of user equipments (UEs). A UE may communicate with a base station via downlink and uplink. The downlink (or forward link) refers to the communication link from the base station to the UE, and the uplink (or reverse link) refers to the communication link from the UE to the base station.

  A base station may transmit data and control information on the downlink and / or receive data and control information on the uplink from the UE. On the downlink, in the transmission from the base station, interference may be recognized due to the transmission from the adjacent base station. On the uplink, transmissions from the UE may cause interference with transmissions from other UEs communicating with neighboring base stations. Interference can degrade performance on both the downlink and uplink.

  Certain aspects of the present disclosure provide a method for wireless communication. This method samples the received signal from one or more receiver antennas to obtain a sampled sequence and analyzes the sampled sequence to detect the primary synchronization sequence (PSS) in the current half frame Calculating SNR metrics based on the detected PSS, combining the calculated SNR metrics with SNR metrics obtained from one or more previous half frames, and combining SNR metrics And obtaining timing information and analyzing the sampled sequence using the timing information to detect a secondary synchronization sequence (SSS).

  Certain aspects of the present disclosure provide an apparatus for wireless communication. The apparatus includes means for sampling a received signal from one or more receiver antennas to obtain a sampled sequence, and analyzing the sampled sequence for a primary synchronization sequence (PSS) in the current half frame. Means for detecting SNR metrics, means for calculating SNR metrics based on detected PSS, and combining the calculated SNR metrics with SNR metrics obtained from one or more previous half frames Means, means for analyzing the combined SNR metrics to obtain timing information, and means for analyzing the sampled sequence using the timing information to detect a secondary synchronization sequence (SSS). In general.

  Certain aspects of the present disclosure provide an apparatus for wireless communication. The apparatus samples a received signal from one or more receiver antennas to obtain a sampled sequence and analyzes the sampled sequence to detect a primary synchronization sequence (PSS) in the current half frame. Calculate a signal-to-noise ratio (SNR) metric based on the detected PSS, and combine the combined SNR metric with the SNR metric based on the PSS detected from one or more previous half frames. At least one processor configured to analyze timing SNR metrics to obtain timing information and analyze the sampled sequence using timing information to detect a secondary synchronization sequence (SSS); Memory combined with two processors. Including Te.

  Certain aspects of the present disclosure provide a computer program product for wireless communication by a user equipment comprising a computer readable medium having instructions stored thereon. The instructions sample received signals from one or more receiver antennas to obtain a sampled sequence, analyze the sampled sequence to detect a primary synchronization sequence (PSS) in the current half frame; Calculate signal-to-noise ratio (SNR) metrics based on the detected PSS and combine the calculated SNR metrics with the SNR metrics based on the PSS detected from one or more previous half frames Can generally be performed by one or more processors for analyzing SNR metrics to obtain timing information and analyzing the sampled sequence using timing information to detect secondary synchronization sequences (SSS) .

1 is a block diagram conceptually illustrating an example of a wireless communication network in accordance with certain aspects of the present disclosure. 1 is a block diagram conceptually illustrating an example frame structure in a wireless communication network, in accordance with certain aspects of the present disclosure. FIG. FIG. 3 illustrates an example format for uplink in Long Term Evolution (LTE) according to some aspects of the present disclosure. 1 is a block diagram conceptually illustrating an example of a Node B communicating with a user equipment device (UE) in a wireless communication network in accordance with certain aspects of the present disclosure. FIG. 6 is an exemplary primary synchronization signal (PSS) sequence and alternate secondary synchronization signal (SSS) diagram having a period of 5 ms according to some aspects of the present disclosure. FIG. 3 illustrates an algorithm that a UE can follow for initial acquisition of a wireless network in accordance with certain aspects of the present disclosure. FIG. 3 illustrates an algorithm that a UE can follow to perform a neighbor cell search in accordance with certain aspects of the present disclosure. FIG. 7 illustrates example operations for detecting a base station of a wireless network in accordance with certain aspects of the present disclosure. FIG. 8 illustrates exemplary components capable of performing the operations shown in FIG.

  In a wireless network, a base station (BS) may transmit a primary synchronization signal (PSS) and a secondary synchronization signal (SSS). These synchronization signals may be used by the UE for cell detection and acquisition. In a typical search operation, a PSS sequence transmitted by a neighboring BS may be found first, and then SSS may be detected. This specification further describes an algorithm for detecting PSS and SSS from the BS.

  The techniques described herein may be used for various wireless communication networks such as CDMA, TDMA, FDMA, OFDMA, SC-FDMA, and other networks. The terms “network” and “system” are often used interchangeably. A CDMA network may implement a radio technology such as Universal Terrestrial Radio Access (UTRA), cdma2000. UTRA includes Wideband CDMA (WCDMA®) and other variants of CDMA. cdma2000 covers IS-2000, IS-95, and IS-856 standards. A TDMA network may implement a radio technology such as Global System for Mobile Communications (GSM). The OFDMA network includes evolved UTRA (E-UTRA), Ultra Mobile Broadband (UMB), IEEE 802.11 (Wi-Fi), IEEE 802.16 (WiMAX), IEEE 802.20, Flash-OFDM (registered trademark). Wireless technology such as can be implemented. UTRA and E-UTRA are part of the Universal Mobile Telecommunication System (UMTS). 3GPP Long Term Evolution (LTE) and LTE-Advanced (LTE-A) are new releases of UMTS that use E-UTRA. UTRA, E-UTRA, UMTS, LTE, LTE-A and GSM are described in documents from an organization named “3rd Generation Partnership Project” (3GPP). cdma2000 and UMB are described in documents from an organization named “3rd Generation Partnership Project 2” (3GPP2). The techniques described herein may be used for the wireless networks and radio technologies mentioned above as well as other wireless networks and radio technologies. For clarity, certain aspects of the techniques are described below for LTE, and LTE terminology is used in much of the description below.

Exemplary Wireless Network FIG. 1 shows a wireless communication network 100, which may be an LTE network. The wireless network 100 may include a number of evolved Node B (eNB) 110 and other network entities. An eNB may be a station that communicates with user equipment devices (UEs) and may also be referred to as a base station, Node B, access point, and so on. Each eNB 110 may provide communication coverage for a particular geographic area. The term “cell” may refer to an eNB's coverage area and / or an eNB subsystem serving this coverage area, depending on the context in which the term is used.

  An eNB may provide communication coverage for macro cells, pico cells, femto cells, and / or other types of cells. The macro cell covers a relatively large geographic area (eg, a few kilometers in radius) and allows unrestricted access by UEs with service subscription. A pico cell covers a relatively small geographic area and allows unrestricted access by UEs with service subscription. A femto cell may cover a relatively small geographic area (eg, home) and a UE that has an association with the femto cell (eg, a UE in a Closed Subscriber Group (CSG), a user at home) Limited access by a UE for example). An eNB for a macro cell may be referred to as a macro eNB. An eNB for a pico cell may be referred to as a pico eNB. An eNB for a femto cell is called a femto eNB or a home eNB. In the example shown in FIG. 1, eNBs 110a, 110b, and 110c may be macro eNBs for macro cells 102a, 102b, and 102c, respectively. eNB 110x may be a pico eNB for pico cell 102x. eNBs 110y and 110z may be femto eNBs for femto cells 102y and 102z, respectively. An eNB may support one or multiple (eg, three) cells.

  Wireless network 100 may also include relay stations. A relay station receives a transmission of data and / or other information from an upstream station (eg, eNB or UE) and transmits a transmission of that data and / or other information to a downstream station (eg, UE or eNB) Station. A relay station may also be a UE that relays transmissions to other UEs. In the example shown in FIG. 1, relay station 110r may communicate with eNB 110a and UE 120r to facilitate communication between eNB 110a and UE 120r. A relay station may be called a relay eNB, a relay, or the like.

  The wireless network 100 may be a heterogeneous network including various types of eNBs, eg, macro eNB, pico eNB, femto eNB, relay, and the like. These different types of eNBs may have different impacts on different transmit power levels, different coverage areas, and interference in the wireless network 100. For example, a macro eNB may have a high transmission power level (eg, 20 watts), while a pico eNB, a femto eNB, and a relay may have a lower transmission power level (eg, 1 watt).

  The wireless network 100 may support synchronous or asynchronous operation. For synchronous operation, the eNB may have similar frame timing and transmissions from different eNBs may be approximately time aligned. For asynchronous operation, eNBs may have different frame timings and transmissions from different eNBs may not be time aligned. The techniques described herein may be used for both synchronous and asynchronous operations.

  Network controller 130 may couple to a set of eNBs and coordinate and control these eNBs. Network controller 130 may communicate with eNB 110 via the backhaul. The eNBs 110 may also communicate with each other directly or indirectly via, for example, a wireless backhaul or wireline backhaul.

  The UEs 120 may be distributed throughout the wireless network 100, and each UE may be fixed or mobile. A UE may also be referred to as a terminal, a mobile station, a subscriber unit, a station, and so on. A UE may be a cellular phone, a personal digital assistant (PDA), a wireless modem, a wireless communication device, a handheld device, a laptop computer, a cordless phone, a wireless local loop (WLL) station, a tablet, and the like. A UE may be able to communicate with macro eNBs, pico eNBs, femto eNBs, relays, and the like. In FIG. 1, a solid line with double arrows indicates a desired transmission between a UE and a serving eNB, which is an eNB designated to serve the UE, on the downlink and / or uplink. A broken line with a double arrow indicates interference transmission between the UE and the eNB.

  LTE utilizes orthogonal frequency division multiplexing (OFDM) on the downlink and single-carrier frequency division multiplexing (SC-FDM) on the uplink. OFDM and SC-FDM partition the system bandwidth into multiple (K) orthogonal subcarriers, also commonly referred to as tones, bins, etc. Each subcarrier may be modulated with data. In general, modulation symbols are sent in the frequency domain with OFDM and in the time domain with SC-FDM. The spacing between adjacent subcarriers can be fixed, and the total number of subcarriers (K) can depend on the system bandwidth. For example, K may be equal to 128, 256, 512, 1024, or 2048, respectively, for a system bandwidth of 1.25, 2.5, 5, 10, or 20 megahertz (MHz). The system bandwidth can also be divided into subbands. For example, the subband may cover 1.08 MHz, one, two, four, eight, or sixteen for a system bandwidth of 1.25, 2.5, 5, 10, or 20 MHz, respectively. There may be subbands.

  FIG. 2 shows a frame structure used in LTE. The downlink transmission timeline can be divided into radio frame units. Each radio frame may have a predetermined duration (eg, 10 milliseconds (ms)) and can be partitioned into 10 subframes with indices from 0 to 9. Each subframe may include two slots. Thus, each radio frame may include 20 slots with indices from 0 to 19. Each slot has L symbol periods, eg, L = 7 symbol periods for a regular cyclic prefix (as shown in FIG. 2), or L = 6 symbols for an extended cyclic prefix. A period can be included. An index of 0-2L-1 may be assigned to 2L symbol periods in each subframe. The available time frequency resources can be divided into resource blocks. Each resource block may cover N subcarriers (eg, 12 subcarriers) in one slot.

  In LTE, the eNB may send a primary synchronization signal (PSS) and a secondary synchronization signal (SSS) for each cell in the eNB. As shown in FIG. 2, the primary synchronization signal and the secondary synchronization signal are respectively transmitted in symbol periods 6 and 5 in each of subframes 0 and 5 of each radio frame having a normal cyclic prefix (CP). Can be sent. The synchronization signal may be used by the UE for cell detection and acquisition. The eNB may send a physical broadcast channel (PBCH) in symbol periods 0 to 3 in slot 1 of subframe 0. PBCH may carry certain system information.

  The eNB may send a Physical Control Format Indicator Channel (PCFICH) during the first symbol period of each subframe, as shown in FIG. PCFICH may carry the number of symbol periods (M) used for the control channel, where M may be equal to 1, 2, or 3, and may vary from subframe to subframe. M may also be equal to 4 for a small system bandwidth, eg, with less than 10 resource blocks. The eNB may send a physical HARQ indicator channel (PHICH) and a physical downlink control channel (PDCCH) during the first M symbol periods of each subframe (see FIG. 2). Not shown). The PHICH may carry information to support a hybrid automatic repeat request (HARQ). The PDCCH may carry information on resource allocation for the UE and control information for the downlink channel. The eNB may send a physical downlink shared channel (PDSCH) during the remaining symbol periods of each subframe. The PDSCH may carry data for UEs scheduled for data transmission on the downlink.

  The eNB may send PSS, SSS, and PBCH at the center of the system bandwidth used by the eNB, 1.08 MHz. The eNB may send PCFICH and PHICH across the entire system bandwidth during each symbol period during which these channels are sent. The eNB may send PDCCH to a group of UEs in some part of the system bandwidth. An eNB may send a PDSCH to a specific UE in a specific part of the system bandwidth. The eNB may send PSS, SSS, PBCH, PCFICH and PHICH to all UEs in a broadcast manner, may send PDCCH to a specific UE in a unicast manner, and may send PDSCH to a specific UE in a unicast manner.

  Several resource elements may be available in each symbol period. Each resource element (RE) may cover one subcarrier in one symbol period and may be used to send one modulation symbol that may be real-valued or complex-valued. Resource elements that are not used for the reference signal in each symbol period may be placed in a resource element group (REG). Each REG may include four resource elements in one symbol period. The PCFICH may occupy four REGs that may be approximately equally spaced across the frequency in symbol period 0. The PHICH may occupy three REGs that may be spread across the frequency in one or more configurable symbol periods. For example, the three REGs for PHICH can all belong to symbol period 0 or can be spread into symbol periods 0, 1, and 2. The PDCCH may occupy 9, 18, 32, or 64 REGs that may be selected from the available REGs during the first M symbol periods. Only some combinations of REGs may be enabled for PDCCH.

  The UE may know the specific REG used for PHICH and PCFICH. The UE may search for various combinations of REGs for PDCCH. The number of combinations to search is generally less than the number of combinations enabled for PDCCH. The eNB may send the PDCCH to the UE in any of the combinations that the UE will search.

  FIG. 2A shows an exemplary format 200A for the uplink in LTE. The available resource blocks for the uplink can be divided into a data section and a control section. The control section may be formed at two edges of the system bandwidth and may have a configurable size. Resource blocks in the control section may be allocated to the UE for transmitting control information. The data section may include all resource blocks that are not included in the control section. The design of FIG. 2A results in a data section that includes consecutive subcarriers that may allow all of the consecutive subcarriers in the data section to be assigned to a single UE.

  In order to send control information to the eNB, UEs can be allocated to resource blocks in the control section. The UE may also be assigned resource blocks in the data section to transmit data to the Node B. The UE may send control information over physical uplink control channels (PUCCH) 210a, 210b in allocated resource blocks in the control section. The UE may transmit data only or both data and control information in physical uplink shared channels (PUSCH) 220a, 220b on assigned resource blocks in the data section. Uplink transmission may be across both slots of the subframe and may hop across the frequency as shown in FIG. 2A.

  A UE may be within the coverage of multiple eNBs. One of these eNBs may be selected to serve the UE. The serving eNB may be selected based on various criteria such as received power, path loss, signal to noise ratio (SNR).

  The UE may operate in a dominant interference scenario where the UE may see significant interference from one or more interfering eNBs. The dominant interference scenario may occur due to limited association. For example, in FIG. 1, UE 120y may be proximate to femto eNB 110y and may have a high received power for eNB 110y. However, UE 120y may not be able to access femto eNB 110y due to limited association, and then macro eNB 110c with lower received power (as shown in FIG. 1) or also lower received power. It may be connected to a femto eNB 110z (not shown in FIG. 1). In that case, UE 120y may see high interference from femto eNB 110y on the downlink and may cause high interference to eNB 110y on the uplink.

  A dominant interference scenario may also occur due to range extension, which is a scenario in which a UE connects to an eNB with a lower path loss and a lower SNR among all eNBs detected by the UE. For example, in FIG. 1, UE 120x may detect macro eNB 110b and pico eNB 110x, and may have lower received power for eNB 110x than eNB 110b. Nevertheless, if the path loss of eNB 110x is lower than the path loss of macro eNB 110b, it may be desirable for UE 120x to connect to pico eNB 110x. This may reduce interference to the wireless network for a given data rate of UE 120x.

  In one aspect, communication in the dominant interference scenario may be supported by operating different eNBs on different frequency bands. A frequency band is a frequency range that can be used for communication, and can be given by (i) a center frequency and bandwidth, or (ii) a lower frequency and a higher frequency. A frequency band is sometimes called a band, a frequency channel, or the like. The frequency bands for different eNBs may be selected such that a UE can communicate with a weaker eNB in a dominant interference scenario while allowing a strong eNB to communicate with its UE. An eNB may be classified as a “weak” eNB or “strong” eNB based on the relative received power of signals from the eNB received at the UE (without being based on the eNB's transmit power level).

  FIG. 3 shows a block diagram of a design of a base station or eNB 110, which may be one of the base stations / eNBs of FIG. 1, and UE 120, which may be one of the UEs of FIG. For the restricted association scenario, eNB 110 may be macro eNB 110c of FIG. 1 and UE 120 may be UE 120y. The eNB 110 may also be some other type of base station. eNB 110 may be equipped with T antennas 334a through 334t, and UE 120 may be equipped with R antennas 352a through 352r, where T ≧ 1 and R ≧ 1.

  At eNB 110, transmission processor 320 may receive data from data source 312 and receive control information from controller / processor 340. The control information may be for PBCH, PCFICH, PHICH, PDCCH, etc. The data may be for PDSCH and the like. Transmit processor 320 may process (eg, encode and symbol map) data and control information to obtain data symbols and control symbols, respectively. Transmit processor 320 may also generate reference symbols for PSS, SSS, and cell specific reference signals, for example. A transmit (TX) multiple-input multiple-output (MIMO) processor 330 may perform spatial processing (eg, precoding) on the data symbols, control symbols, and / or reference symbols, where applicable, The output symbol stream may be provided to T modulators (MODs) 332a through 332t. Each modulator 332 may process a respective output symbol stream (eg, for OFDM) to obtain an output sample stream. Each modulator 332 may further process (eg, convert to analog, amplify, filter, and upconvert) the output sample stream to obtain a downlink signal. T downlink signals from modulators 332a through 332t may be transmitted via T antennas 334a through 334t, respectively.

  At UE 120, antennas 352a-352r may receive downlink signals from eNB 110 and may provide received signals to demodulators (DEMOD) 354a-354r, respectively. Each demodulator 354 may adjust (eg, filter, amplify, downconvert, and digitize) a respective received signal to obtain input samples. Each demodulator 354 may further process input samples (eg, OFDM) to obtain received symbols. MIMO detector 356 may obtain received symbols from all R demodulators 354a-354r, perform MIMO detection on the received symbols, if applicable, and provide detected symbols. Receive processor 358 processes (eg, demodulates, deinterleaves, and decodes) the detected symbols, provides decoded data of UE 120 to data sink 360, and provides decoded control information to controller / processor 380. obtain.

  On the uplink, at UE 120, transmit processor 364 may receive and process data (eg, for PUSCH) from data source 362 and control information from controller / processor 380 (eg, for PUCCH). Can be received and processed. Transmit processor 364 may also generate reference symbols for the reference signal. Symbols from transmit processor 364 may be precoded by TX MIMO processor 366, where applicable, and further processed by modulators 354a-354r (eg, for SC-FDM, etc.) and transmitted to eNB 110. At eNB 110, the uplink signal from UE 120 is received by antenna 334, processed by demodulator 332, detected by MIMO detector 336 when applicable, and further processed by receive processor 338 to provide UE 120 The decrypted data and control information sent by can be obtained. The receiving processor 338 may provide the decoded data to the data sink 339 and the decoded control information to the controller / processor 340.

  Controllers / processors 340, 380 may direct the operation at eNB 110 and the operation at UE 120, respectively. Processor 340 and / or other processors and modules at base station 110 may perform or direct the execution of various processes for the techniques described herein. Processor 380 and / or other processors and modules at UE 120 may also perform or direct the execution of the functional blocks shown in FIG. 7 and / or other processes for the techniques described herein. obtain. Memories 342 and 382 may store data and program codes for base station 110 and UE 120, respectively. A scheduler 344 may schedule UEs for data transmission on the downlink and / or uplink.

  In LTE, the cell identifier ranges from 0 to 503. The synchronization signal is transmitted in the central 62 resource elements (RE) centered on the DC tone to help detect the cell. The synchronization signal comprises two parts, a primary synchronization signal (PSS) and a secondary synchronization signal (SSS).

FIG. 4 illustrates an exemplary PSS sequence 402 and alternating SSS sequences 404 ₀ , 404 ₁ having a period of 5 ms, according to some aspects of the present disclosure. The PSS allows the UE to obtain a frame timing modulo 5ms and part of the physical layer cell identifier (cell ID), and in particular cell ID modulo 3. There are three different PSS sequences including each sequence mapping to an independent group of 168 cell IDs. Based on the Zadoff-Chu (ZC) sequence, a PSS sequence is selected from one of three sequences based on PSS index = cell ID modulo 3. The same sequence is transmitted every 5 ms as shown in FIG.

  SSS is used by the UE to detect LTE frame timing modulo 10 ms and to obtain a cell ID. As shown in FIG. 4, the SSS is transmitted twice in each 10 ms radio frame. SSS sequences are based on maximum length sequences called M-sequences, and each SSS sequence is constructed by interleaving a 2-length-31 binary phase shift keying (BPSK) modulation sequence in the frequency domain. The two codes are two different cyclic shifts of a single length 31M sequence. The M-sequence cyclic shift index is derived from a function of the physical layer cell ID group. The two codes appear alternately in the first SSS transmission and the second SSS transmission in each radio frame.

  In other words, two sequences of cell IDs appearing alternately every 5 ms are transmitted. The SSS sequence first selects a sequence from a set of 168 different sequences (various sets of subframes 0 and 5) based on the SSS index (= floor (cell ID / 3)) and then PSS. Obtained by scrambling the selected sequence using a sequence that is a function of the index. Thus, while searching for an SSS, the UE need only search a maximum of 168 sequences if the PSS index is known.

  The interval between the PSS and SSS allows the UE to distinguish between extended cyclic prefix (CP) and normal CD mode and between TDD (time division duplex) and FDD (frequency division duplex) modes. Enable.

  In a typical search operation, first a PSS sequence transmitted by a neighboring eNB is found (ie, the timing and PSS index are determined), and then SSS detection is performed for the PSS index found around the determined timing. Is called.

  For both PSS detection and SSS detection, samples across multiple bursts can be used to improve detection opportunities and reduce false positive rates. Using multiple bursts allows time diversity. Placing each burst at an interval improves time diversity, but increases detection time.

Initial Acquisition and Proximity Search Algorithm for Wireless Networks Embodiments of the present disclosure provide base station physics for wireless networks (eg, eNBs in LTE networks) by using synchronization signals (eg, PSS and SSS) supplied by eNBs. A technique for detecting the layer cell ID is realized. This specification further describes the modem baseband algorithm in which PSS and SSS from the eNB are detected.

  For initial acquisition of an eNB, embodiments of the present disclosure implement a technique for finding an LTE signal having a center frequency in the band of interest. The UE may detect at least the following unknown information during initial acquisition: frame timing, physical layer ID, cell ID group, and cyclic prefix (CP) length used in the frame. The UE may use two synchronization signals, PSS and SSS, that can be transmitted every 5 ms by the eNB as described above to facilitate detection and estimation of the above quantities.

  FIG. 5 illustrates an algorithm that a UE can follow for initial acquisition of cells in a wireless network, according to some aspects of the present disclosure. First, at 501, the UE samples and samples a received signal from one or more receiver antennas (eg, at least 5 ms samples per receiver antenna, or samples downsampled to 1.92 MHz). ) May be acquired. The UE may store the complex input samples in a buffer of at least 9600 samples. At 502, the UE may perform PSS detection in the current half frame (HF) by generating detection metrics based on three reference PSS sequences and all 9600 timing hypotheses. In some embodiments, at 503, some frequency hypotheses (eg, phase gradient or phase rotation in time) are applied to the signal prior to PSS detection to eliminate the risk of failing to detect a low SNR signal. May be. PSS correlation may be performed for each hypothesis, and timing detection may be performed for the hypothesis with better metrics.

  At 504, the UE calculates an SNR metric based on the detected PSS and the calculated SNR metric (eg, to improve reliability) and an SNR metric obtained from one or more previous HFs You may combine noncoherently. At 506, the UE may select the top M peaks by sorting the PSSs from HF in descending order of PSS SNR after combining each half frame. At 507, the UE may analyze the combined SNR metrics to obtain timing information. After each half frame (eg, 5 ms), the UE performs the following steps on each of the M candidates: frequency offset estimation based on PSS (508), frequency compensation of samples based on frequency offset estimation (510), and SSS detection (512) may be performed.

  As shown, the UE may estimate the frequency offset by evaluating SNR metrics based on the detected PSS and perform frequency compensation of the sampled sequence based on the estimated frequency offset. Therefore, the frequency can be compensated before SSS detection. The UE performs SSS detection every half frame by analyzing the sample sequence (or frequency compensated sampled sequence) using timing information, and finally (for example, to improve reliability) The union of the cells detected over the half frame may be obtained. If, at 514, the SSS detection SNR metric exceeds a threshold at any point, the cell ID, its CP, and timing may be considered detected and PBCH decoding may be attempted for this candidate (516 ). In some embodiments, the joint frequency offset may be calculated 515 by evaluating SNR metrics based on the detected PSS and the detected SSS prior to PBCH decoding.

  However, if the SSS detection fails to obtain a candidate (eg, the SSS detection SNR metric did not exceed the threshold), the UE determines whether there are remaining candidates out of the M candidates (517 ), The above algorithm may be continued. If there are no candidates for SSS detection after the M candidates are gone, the UE may continue the above algorithm until there are no non-coherent combinations of PSS SNR metrics in N HFs (518). If no cell is found after all the above SSS detection attempts have been completed, the UE may determine that no cell is present on the carrier frequency (520).

  After successful initial acquisition, the UE may be camped on to the LTE cell (ie, serving cell). With respect to proximity search, embodiments of the present disclosure provide techniques for finding an LTE cell that is different from the cell where the UE is camped on, thereby allowing the UE to monitor measurements of various neighboring cells. Is realized.

  FIG. 6 illustrates an algorithm that a UE can follow to perform a neighbor cell search in accordance with certain aspects of the present disclosure. First, at 501, the UE samples and samples a received signal from one or more receiver antennas (eg, at least 5 ms samples per receiver antenna, or samples downsampled to 1.92 MHz). ) May be acquired. The UE may store the complex input samples in a buffer of at least 9600 samples. At 502, the UE may perform PSS detection in the current HF by generating detection metrics based on three reference PSS sequences and all 9600 timing hypotheses. At 504, the UE may calculate SNR metrics based on the detected PSS and may combine the calculated SNR metrics with SNR metrics obtained from one or more previous HFs incoherently. In some embodiments, SSS detection may be performed on a per-HF basis, similar to the initial acquisition algorithm shown in FIG.

  In some embodiments, after N HFs are non-coherently combined (verified at 602), SSS detection may be attempted on the candidate peak as described above. For example, the UE may sort the PSS from HF in descending order of PSS SNR, select the top M peaks (506), and perform SSS detection for each of the M candidates (512). At 514, if the SSS detection SNR metric exceeds a threshold at any point, the cell ID, its CP, and timing may be considered detected. However, if no candidate is obtained after the M SSS detection attempts are completed, the UE may determine that there is no cell on that carrier frequency (604).

  FIG. 7 illustrates an example operation 700 for detecting a base station of a wireless network in accordance with certain aspects of the present disclosure. Operation 700 may be performed by a UE, for example. Detecting the base station may be performed for initial acquisition of the base station or while performing a proximity search. At 702, the UE may sample received signals from one or more receiver antennas to obtain a sampled sequence. For example, the UE may sample at least 5 ms samples per receiver antenna or downsampled to 1.92 MHz.

  At 704, the UE may analyze the sampled sequence to detect the PSS in the current half frame. At 706, the UE may calculate SNR metrics based on the detected PSS. At 708, the UE may combine the calculated SNR metrics with SNR metrics obtained from one or more previous half frames. For example, the UE may combine the calculated SNR metrics non-coherently with the SNR metrics obtained from one or more previous HFs to improve reliability.

  At 710, the UE may analyze the combined SNR metrics to obtain timing information. In some aspects, analyzing the combined SNR metrics is based on sorting and sorting SNR metrics based on the calculated SNR metrics and PSS detected from one or more previous half frames. Maintaining one or more of the largest SNR metrics and analyzing the first SNR metric of the largest SNR metrics to obtain timing information.

  At 712, the UE detects the SSS by analyzing the sampled sequence using the timing information. In some aspects, the UE may estimate the frequency offset by evaluating a first SNR metric of maximum SNR metrics, and may sample based on the estimated frequency offset before detecting the SSS. The frequency compensation of the generated sequence may be performed.

  In some aspects, the UE may calculate an SNR metric based on the detected SSS, and compare the SNR metric based on the detected SSS to a threshold. If the SNR metric based on the detected SSS is less than the threshold, the UE is based on the second of the largest SNR metrics based on the PSS detected from one or more previous half frames. SSS may be detected.

  After detecting the SSS, the UE may calculate a joint frequency offset by evaluating SNR metrics based on the detected PSS and the detected SSS. In some aspects, SSS detection may be performed every half frame. In some aspects, SSS detection may be performed at the end of a combination of SNR metrics based on PSS over one or more half frames.

  The operations 700 described above may be performed by any suitable component or other means capable of performing the corresponding functions of FIG. For example, operation 700 shown in FIG. 7 corresponds to component 700A shown in FIG. 7A. In FIG. 7A, transceiver (TX / RX) 701A may receive signals at one or more receiver antennas. Sampling unit 702A may sample the received signal to obtain a sampled sequence. Analysis unit 704A may analyze the sampled sequence to detect the PSS in the current half frame. Calculation unit 706A may calculate SNR metrics based on the detected PSS. Combining unit 708A may combine the calculated SNR metrics with SNR metrics obtained from one or more previous half frames. Analysis unit 710A may analyze the combined SNR metrics to obtain timing information. Analysis unit 712A may analyze the sampled sequence using the timing information to detect SSS.

  Various operations of the methods described above may be performed by any suitable means capable of performing the corresponding function. These means include, but are not limited to, various hardware and / or software component (s) and / or module (s) including a circuit, application specific integrated circuit (ASIC), or processor. obtain. For example, the means for transmitting or the means for sending include the transmitter of UE 120, modulator 354, and / or antenna 352 shown in FIG. 3, or the transmitter of eNB 110, modulator 332, and / or shown in FIG. An antenna 334 may be provided. Means for receiving may comprise the receiver of UE 120, demodulator 354, and / or antenna 352 shown in FIG. 3, or the receiver, demodulator 332, and / or antenna 334 of eNB 110 shown in FIG. The means for processing, the means for determining, the means for sampling, and / or the means for canceling may comprise a processing system, which is shown in FIG. , A receiving processor 338, or a controller / processor 340, or a receiving processor 358, a transmitting processor 364, or a controller / processor 380 of the UE 120 shown in FIG.

  Those of skill in the art will understand that information and signals may be represented using any of a variety of different technologies and techniques. For example, data, instructions, commands, information, signals, bits, symbols, and chips that may be referred to throughout the above description are voltages, currents, electromagnetic waves, magnetic fields or magnetic particles, light fields or optical particles, or any of them Can be represented by a combination.

  Further, those skilled in the art will appreciate that the various exemplary logic blocks, modules, circuits, and algorithm steps described in connection with the disclosure herein can be implemented as electronic hardware, computer software, or a combination of both. Let's be done. To clearly illustrate this interchangeability of hardware and software, various illustrative components, blocks, modules, circuits, and steps have been described above generally in terms of their functionality. Whether such functionality is implemented as hardware or software depends upon the particular application and design constraints imposed on the overall system. Those skilled in the art can implement the described functionality in a variety of ways for each particular application, but such implementation decisions should not be construed as departing from the scope of the present disclosure.

  Various exemplary logic blocks, modules, and circuits described in connection with the disclosure herein include general purpose processors, digital signal processors (DSPs), application specific integrated circuits (ASICs), field programmable gate arrays (FPGAs). ) Or other programmable logic device, individual gate or transistor logic, individual hardware components, or any combination thereof designed to perform the functions described herein. A general purpose processor may be a microprocessor, but in the alternative, the processor may be any conventional processor, controller, microcontroller, or state machine. The processor may be implemented as a combination of computing devices, eg, a combination of a DSP and a microprocessor, a plurality of microprocessors, one or more microprocessors associated with a DSP core, or any other such configuration. You can also.

  The method or algorithm steps described in connection with the disclosure herein may be implemented directly in hardware, software modules executed by a processor, or a combination of the two. A software module resides in RAM memory, flash memory, ROM memory, EPROM memory, EEPROM memory, registers, hard disk, removable disk, CD-ROM, or any other form of storage medium known in the art. can do. An exemplary storage medium is coupled to the processor such that the processor can read information from, and / or write information to, the storage medium. In the alternative, the storage medium may be integral to the processor. The processor and the storage medium can reside in the ASIC. The ASIC can reside in the user terminal. In the alternative, the processor and the storage medium may reside as discrete components in a user terminal.

  In one or more exemplary designs, the functions described can be implemented in hardware, software, firmware, or any combination thereof. When implemented in software, the functions can be stored on or transmitted over as one or more instructions or code on a computer-readable medium. Computer-readable media includes both computer storage media and computer communication media including any medium that facilitates transfer of a computer program from one place to another. A storage media may be any available media that can be accessed by a general purpose or special purpose computer. By way of example, and not limitation, such computer-readable media may be RAM, ROM, EEPROM, CD-ROM, or other optical disk storage, magnetic disk storage or other magnetic storage device, or any desired form in the form of instructions or data structures. Any other medium that can be used to carry or store the program code means and that can be accessed by a general purpose or special purpose computer or general purpose or special purpose processor can be provided. In addition, any connection is properly referred to as a computer-readable medium. For example, software sends from a website, server, or other remote source using coaxial cable, fiber optic cable, twisted pair, digital subscriber line (DSL), or wireless technologies such as infrared, wireless, and microwave Where included, coaxial technology, fiber optic cable, twisted pair, DSL, or wireless technologies such as infrared, radio, and microwave are included in the definition of media. As used herein, a disk and a disc are a compact disc (CD), a laser disc, an optical disc, a digital versatile disc (DVD). , Floppy disks and Blu-ray discs, which typically reproduce data magnetically and discs optically data with a laser To play. Combinations of the above should also be included within the scope of computer-readable media.

  The previous description of the disclosure is provided to enable any person skilled in the art to make or use the disclosure. Various modifications to this disclosure will be readily apparent to those skilled in the art and the generic principles defined herein may be applied to other variations without departing from the spirit or scope of this disclosure. Accordingly, the present disclosure is not intended to be limited to the examples and designs described herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims (20)

A method for wireless communication by a user equipment (UE) comprising:
Sampling a received signal from one or more receiver antennas to obtain a sampled sequence;
Analyzing the sampled sequence to detect a primary synchronization sequence (PSS) in a current half frame;
Calculating a signal to noise ratio (SNR) metric based on the detected PSS;
Combining the calculated SNR metrics with PNR-based SNR metrics detected from one or more previous half frames;
Analyzing the combined SNR metrics to obtain timing information;
Analyzing the sampled sequence using the timing information to detect a secondary synchronization sequence (SSS).   The method of claim 1, wherein the SSS detection is performed every half frame.   The method of claim 1, wherein SSS detection is performed at the end of a combination of SNR metrics based on PSS over one or more half frames.   The method of claim 3, wherein the PSS detection and the SSS detection are performed to identify LTE cells proximate to a serving cell.   The method of claim 1, further comprising calculating a joint frequency offset by evaluating SNR metrics based on the detected PSS and the detected SSS. Analyzing the combined SNR metrics includes
Sorting the calculated SNR metric and the SNR metric based on the PSS detected from the one or more previous half frames;
Holding one or more of the maximum SNR metrics based on the sorting;
2. The method of claim 1, comprising analyzing a first SNR metric of the maximum SNR metrics to obtain the timing information. Estimating a frequency offset by evaluating the first SNR metric of maximum SNR metrics;
7. The method of claim 6, further comprising performing frequency compensation of the sampled sequence based on the estimated frequency offset prior to detecting the SSS. Calculating SNR metrics based on the detected SSS;
7. The method of claim 6, further comprising comparing the SNR metric based on the detected SSS to a threshold value. The SNR metric based on the detected SSS is less than the threshold, and the method comprises:
9. The method of claim 8, further comprising detecting the SSS based on other PSS SNR metrics obtained and sorted from one or more previous half frames. An apparatus for wireless communication by a user equipment (UE),
Means for sampling a received signal from one or more receiver antennas to obtain a sampled sequence;
Means for analyzing the sampled sequence to detect a primary synchronization sequence (PSS) in a current half frame;
Means for calculating a signal to noise ratio (SNR) metric based on the detected PSS;
Means for combining the calculated SNR metrics with PSS-based SNR metrics detected from one or more previous half frames;
Means for analyzing the combined SNR metrics to obtain timing information;
Means for analyzing the sampled sequence using the timing information to detect a secondary synchronization sequence (SSS).   The apparatus of claim 10, wherein SSS detection is performed every half frame.   The apparatus of claim 10, wherein SSS detection occurs at the end of a combination of SNR metrics based on PSS over one or more half frames.   The apparatus of claim 12, wherein PSS detection and SSS detection are performed to identify LTE cells proximate to a serving cell.   The apparatus of claim 10, further comprising means for calculating a joint frequency offset by evaluating SNR metrics based on the detected PSS and the detected SSS. Means for analyzing the combined SNR metrics are:
Means for sorting the SNR metrics based on the calculated SNR metrics and the PSS detected from the one or more previous half frames;
Means for maintaining one or more of the maximum SNR metrics based on the sorting;
11. The apparatus of claim 10, comprising: means for analyzing a first SNR metric of the maximum SNR metrics to obtain the timing information. Means for estimating a frequency offset by evaluating the first SNR metric of the maximum SNR metrics;
16. The apparatus of claim 15, further comprising means for performing frequency compensation of the sampled sequence based on the estimated frequency offset prior to detecting the SSS. Means for calculating SNR metrics based on the detected SSS;
The apparatus of claim 15, further comprising means for comparing the SNR metric based on the detected SSS with a threshold.   Means for detecting the SSS based on other PSS SNR metrics obtained from and sorted from one or more frames when the SNR metric based on the detected SSS is less than the threshold The apparatus of claim 17, further comprising: An apparatus for wireless communication by a user equipment (UE),
Sampling a received signal from one or more receiver antennas to obtain a sampled sequence, analyzing the sampled sequence to detect a primary synchronization sequence (PSS) in a current half-frame; Calculating a signal-to-noise ratio (SNR) metric based on the detected PSS, combining the calculated SNR metric with an SNR metric based on the PSS detected from one or more previous half-frames; Analyzing at least one SNR metric to obtain timing information and using the timing information to analyze the sampled sequence to detect a secondary synchronization sequence (SSS);
An apparatus for wireless communication comprising a memory coupled to the at least one processor. A computer program product for wireless communication by a user equipment comprising a computer readable medium having instructions stored thereon, the instructions comprising:
Sample received signals from one or more receiver antennas to obtain a sampled sequence;
Analyzing the sampled sequence to detect a primary synchronization sequence (PSS) in the current half-frame;
Calculating a signal-to-noise ratio (SNR) metric based on the detected PSS;
Combining the calculated SNR metrics with PNR-based SNR metrics detected from one or more previous half frames;
Analyzing the combined SNR metrics to obtain timing information;
A computer program product executable by one or more processors to analyze the sampled sequence using the timing information to detect a secondary synchronization sequence (SSS).

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